High-temperature polar clusters in perovskite-type relaxor ferroelectrics and their response to an electric field

弛豫铁电体是一种局部非均匀材料，由于其优异的介电、机电和电光响应而受到广泛关注。这种独特的弛豫性质与分散在整体立方结构中的极性纳米团簇的存在有关。了解实际的极性原子聚类及其与弛豫性质的相互作用对凝聚态物理学家和材料科学家来说是一个巨大的挑战。本项目旨在分析在介电常数最大值温度以上的温度下形成极性纳米区的优先极性原子位移和耦合过程。为此，将共振拉曼光谱应用于670 ~ 80 K温度范围内的模型化合物（化学计量和ba掺杂的PbSc0.5Ta0.5O3和PbSc0.5Nb0.5O3），通过增强的纵向光学模式的变化来分析极性物种的平均尺寸和分布的演变。此外，将在850 ~ 80k的外电场下用原位常规拉曼光谱研究相同化合物，以阐明相干极性原子位移的首选晶体学方向和极性团簇的可切换性。此外，利用拉曼光谱和光学椭偏仪分析了新合成的含ru的PbSc0.5Ta0.5O3、PbSc0.5Nb0.5O3和0.9PbZn1/3Nb2/3O3-PbTiO3的声子态和价电子态的温度演化。

Relaxor ferroelectrics are locally inhomogeneous materials that have been attracted tremendous attention due to their exceptional dielectric, electromechanical and electrooptic response. The unique relaxor properties are related to the existence of polar nanoclusters dispersed in the overall cubic structure. The understanding of the actual polar atomic clustering and its interplay with the relaxor properties is a great challenge to condensed-matter physicists and materials scientists. This project aims to analyze the preferential polar atomic shifts and coupling processes to form polar nanoregions at temperatures above the temperature of the dielectric permittivity maximum. For the purpose, resonance Raman spectroscopy will be applied to model compounds (stoichiometric and Ba-doped PbSc0.5Ta0.5O3 and PbSc0.5Nb0.5O3) in the temperature range 670 – 80 K to analyze the evolution of the mean size and distribution of polar species via the changes in the enhanced longitudinal optical modes. Further, the same compounds will be studied by in situ conventional Raman spectroscopy under an external electric field at temperatures between 850 and 80 K to elucidate the preferred crystallographic direction of coherent polar atomic displacements and the switchability of polar clusters. In addition, the temperature evolution of phonon and valence-electron states of newly synthesized Ru-containing PbSc0.5Ta0.5O3, PbSc0.5Nb0.5O3 and 0.9PbZn1/3Nb2/3O3-PbTiO3 will be analyzed by Raman spectroscopy and optical ellipsometry.